A simple and sensitive analytical method for the determination of antimony in environmental and biological samples.

The results of a study and application of leucocrystal violet for the determination of antimony in parts per million levels is described here. The proposed method is based on the reaction of antimony(III) with acidified potassium iodate to liberate iodine. The liberated iodine selectively oxidizes leucocrystal violet to crystal violet dye. The formed dye shows maximum absorbance at 590 nm. The color system obeys Beer's law in the concentration range from 0.4 - 3.6 microg antimony per 25 ml of final solution. The molar absorptivity and Sandell's sensitivity were found to be 7.32 x 10(5) l mol(-1) cm(-1) and 0.0016 microg cm(-2), respectively. All variables were studied in order to optimize the reaction. The proposed method is satisfactorily applicable for the analysis of antimony in various environmental and biological samples. The method is simple, highly sensitive, accurate and reliable.     

New Method for the Synthesis of Benzyl Alkyl Ethers Mediated by FeSO4

The synthesis of benzyl alkyl ethers from benzyl bromides and alcohols using FeSO₄ as a recoverable and reusable mediator has been described without use of base and cosolvent under mild conditions.     

KHSO4: a highly efficient and reusable heterogeneous catalyst for hydroarylation of styrenes

Abstract  

Hydroarylation of styrenes with arenes/heteroarenes using KHSO₄ (10 mol%) as an efficient heterogeneous catalyst is described. High conversion and selectivity (>99%) were observed for hydroarylation of styrenes with 2-naphthol at reflux temperature of 1,2-dichloroethane. Yields were quantitative with all styrenes. Moderate to good conversions and selectivities were achieved with other aromatics and heteroaromatics under the same conditions. Regeneration and reusability of KHSO₄ were demonstrated. Addition of a trace amount of water could help to reactivate the KHSO₄ through dispersion and to facilitate the hydroarylation reaction.     

Investigations on regio‐ and stereoselectivities in cycloadditions involving α‐ (3‐pyridyl)‐N‐phenylnitrone: Development of an efficient route to novel nicotine analogs

Thermal reactions of hitherto α‐(3‐pyridyl)‐N‐phenylnitrone ( 1 ) with mono‐substituted electron‐rich and electron‐neutral dipolarophiles are regio‐, and stereo‐selective (exo‐selective), controlled by LUMO ‐ dipole ‐ HOMO‐ dipolarophile interaction, and furnish syn‐5‐substituted‐3‐(3‐pyridyl)‐isoxazolidines ( 5 ) in high yields. With electron deficient dipolarophiles such as acrylonitrile there is observed a loss of regioselectivity as well as stereoselectivity and the regioselectivity is reversed in reactions with methyl vinyl ketone and methyl acrylate, due to intervention of HOMO‐dipole ‐ LUMO‐dipolarophile interaction, affording 4‐substi‐tuted‐3‐(3‐pyridyl)‐isoxazolidines ( 7 ) as major products. Reactions of nitrone ( 1 ) with disubstituted dipolarophiles such as methyl methacrylate and ethyl coronate furnish methyl syn‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐5‐carboxylate ( 8 ) and ethyl anti‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐4‐carboxylate ( 10 ), respectively, in high yields. Reaction with N‐Phenylmaleimide affords novel isoxazolidino‐pyrro‐lidinediones bearing a 3‐pyridyl moiety ( 11, 12 ). A mechanistic rationalization of the obtained results in terms of electronic, steric and secondary interactions is proffered.     

Facile C21 functionalization through a novel functional group transfer reaction in 16 alpha,17 alpha-epoxy-3 beta-hydroxypregn-5-en-20-one and its applications

A novel functional group transfer reaction in 16 alpha,17 alpha-epoxy-3 beta-hydroxypregn-5-en-20-one by treatment with dry HCl affords 21-chloro-3 beta-hydroxy-pregn-5,16-dien-20-one, which has been utilized to obtain a number of C21-substituted derivatives.     

Better biomolecule thermodynamics from kinetics

Protein stability is measured by denaturation: When solvent conditions are changed (e.g., temperature, denaturant concentration, or pH) the protein population switches between thermodynamic states. The resulting denaturation curves have baselines. If the baselines are steep, nonlinear, or incomplete, it becomes difficult to characterize protein denaturation. Baselines arise because the chromophore probing denaturation is sensitive to solvent conditions, or because the thermodynamic states evolve structurally when solvent conditions are changed, or because the barriers are very low (downhill folding). Kinetics can largely eliminate such baselines: Relaxation of chromophores, or within thermodynamic states, is much faster than the transition over activation barriers separating states. This separation of time scales disentangles population switching between states (desired signal) from chromophore or population relaxation within states (baselines). We derive simple formulas to extract unfolding thermodynamics from kinetics. The formulas are tested with model data and with a difficult experimental test case: the apparent two-state folder PI3K SH3 domain. Its melting temperature T(m) can be extracted reliably by our "thermodynamics from kinetics approach," even when conventional fitting is unreliable.     

Analytical Method Validation and Determination of Iron and Phosphorus in Vegetable Oil by Inductively Coupled Plasma–Mass Spectrometry with Microwave Assisted Digestion

Inductively coupled plasma–mass spectrometric determination of iron and phosphorus in three vegetable oils (soybean, coconut, and sunflower) was validated for the intermediate precision, trueness, linearity, and quantitation limit. The overall precision (n?=?5) for the analytes, which were above the method’s practical limit of quantification, were less than 2% relative standard deviation and the same as the laboratory control, NIST-SRM-1849a. Trueness was demonstrated with spike recoveries of the analytes in all vegetable oils at limit of quantification-level spiking. Although good linearity (regression coefficient greater than 0.9990) obtained, the recovery of phosphorus (156–189%) was high, possibly due to oil matrix enhancement, compared to the recovery of iron (91–106%). For soybean oil, sunflower oil, coconut oil, and medium chain triglycerides, the concentrations (mg/kg) of iron were in the range of 0.10–1.47, 0.09–1.51, 0.20–0.35, and 0.09–0.13, respectively. Similarly, phosphorus concentrations (mg/kg) were in the range of 0.77–124.56, 0.49–125.57, 0.52–9.72, and 0.85–11.90, respectively. The study achieved considerably low instrument-based practical limits of quantification for iron (0.005?mg/kg) and phosphorus (0.05?mg/kg), which are fivefold lower than the AOAC Official Method 2015.06. The high instrument sensitivity and selectivity of the method allow the determination of trace levels of iron and phosphorus in vegetable oils with good precision and trueness.     

All Solid State Chromium(III) Selective Potentiometric Sensor Based on 2‐(1‐(2‐((3‐(2‐Hydroxyphenyl)‐1H‐pyrozol‐1‐yl)methyl)benzyl)‐1H‐pyrazol‐3‐yl)phenol

Highly selective all solid state electrochemical sensor based on a synthesized compound i.e. 2‐(1‐(2‐((3‐(2‐hydroxyphenyl)‐1H‐pyrozol‐1‐yl)methyl)benzyl)‐1H‐pyrazol‐3‐yl)phenol (I) as an ionophore has been prepared and investigated for the selective quantification of chromium(III) ions. The effect of various plasticizers, viz. dibutyl phosphonate (DBP), dibutyl(butyl) phosphonate (DBBP), nitrophenyl octyl ether (NPOE), tris‐(2‐ethylhexyl)phosphonate (TEP), tri‐butyl phosphonate (TBP), dioctyl phthalate (DOP), dioctyl sebacate (DOS), benzyl acetate (BA) and acetophenone (AP) along with anion excluders NaTPB (sodium tetraphenyl borate) and KClTPB (potassium(tetrakis‐4‐chlorophenyl)borate was also studied. The optimum composition of the best performing membrane contained (I):KClTPB:NPOE:PVC in the ratio 15 : 3 : 40 : 42 w/w. The sensor exhibited near Nernstian slope of 20.1±0.2 mV/decade of activity in the working concentration range of 1.2×10^?7–1.0×10^?1 M, and in a pH range of 3.8–4.5. The sensor exhibited a fast response time of 10 s and could be used for about 5 months without any considerable divergence in potentials. The proposed sensor showed very good selectivity over most of the common cations including Na⁺, Li⁺, K⁺, Cu²⁺, Sr²⁺, Ni²⁺, Co²⁺, Ba²⁺, Hg²⁺, Pb²⁺, Zn²⁺, Cs⁺, Mg²⁺, Cd²⁺, Al³⁺, Fe³⁺and La³⁺. The activity of Cr(III) ions was successfully determined in the industrial waste samples by using this sensor.     

A review on synthetic approaches of heterocycles via insertion-cyclization reaction

Abstract

Heterocyclic compounds have a wide range of applications: they are predominant among the type of compounds used as pharmaceuticals, agrochemicals, fine chemicals, electronic components, polymers, and veterinary products. There is a vast scope to develop new heterocyclic compounds considering the high yield, low waste, and green synthesis. In this review, we have described the synthesis of heterocycles via insertion and cyclization which is achieved in recent years with the ideas, challenges, and milestone reactions.